I think I found a fix for the memory leak issue on gRPC module
Roman Arutyunyan
arut at nginx.com
Wed May 22 14:14:26 UTC 2024
Hi,
Indeed there's a problem there. We have similar problems in other places as
well. Attached is a patch that fixes all I could find.
I did some testing for the sub_filter with the following config. Small buffers
exaggerate the problem.
http {
server {
listen 8000;
location / {
root html;
output_buffers 2 128;
sub_filter 1 2;
sub_filter_types *;
sub_filter_once off;
}
}
}
Retrieving a 10m file resulted in 7304 (patched) vs 1317704 (unpatched) bytes
allocated from the request pool. With the default output_buffers (2 32768),
it's 79880 vs 84040.
On Thu, May 02, 2024 at 07:59:44AM +0000, Pavel Pautov via nginx-devel wrote:
> Hi Sangmin,
>
> Your analysis looks correct. Client streaming RPCs can lead to unbound accumulation of ngx_chain_t objects (although, at very slow rate). Gzip module had a similar issue (https://trac.nginx.org/nginx/ticket/1046).
> Attaching somewhat simplified patch based on yours. I was able to reproduce the issue locally and the patch fixes it.
>
> From: nginx-devel <nginx-devel-bounces at nginx.org> On Behalf Of Sangmin Lee
> Sent: Thursday, April 4, 2024 19:29
> To: nginx-devel at nginx.org
> Subject: I think I found a fix for the memory leak issue on gRPC module
>
> CAUTION: This email has been sent from an external source. Do not click links, open attachments, or provide sensitive business information unless you can verify the sender's legitimacy.
>
> I am sending this mail again because I did a mistake while I was writing a mail. I didn't know, in gmail, "Ctrl - Enter" would send a mail immediately even without a title!
> I am sorry for that, so I am sending again.
>
> Hello,
>
> I think I found the main cause of the memory leak issue when using gRPC stream so I made a patch for it.
> Please find the test scenario and details here -- This is what I wrote.:
> https://trac.nginx.org/nginx/ticket/2614
> After I changed the memory pool totally on nginx and tested our workload -- long-lived gRPC streams with many connections -- using Valgrind and massif, I was able to find what brought up the memory leak issue.
> like the picture below.
>
> [cid:image001.png at 01DA9C29.C792CD90]
> ( I am not sure whether this picture will be sent properly )
>
> After I patched one part, it seems okay now I have tested it for 1 week with out workload.
>
> [cid:image002.png at 01DA9C29.C792CD90]
> ( I am not sure whether this picture will be sent properly )
>
> But because I am not familiar with Mercurial, I couldn't find a way to create PR like on github. I guess this mailing list is for this patch.
> From my point of view, it is more like a workaround and I think the way of using ngx_chain_add_copy() or itself needs to be changed because it allocates a ngx_chain_t structure using ngx_alloc_chain_link() but inside of that, it just copies pointer, like cl->buf = in->buf;
> so this ngx_chain_t instance should be dealt with differently unlike other ngx_chain_t instances.
> But I am quite new to nginx codes so my view might be wrong.
> Anyhow, please go over this patch and I would like to further talk here.
>
> --------------------------------------------------------------------------------------------------------------------------------------------
>
> diff --git a/src/http/modules/ngx_http_grpc_module.c b/src/http/modules/ngx_http_grpc_module.c
> index dfe49c586..1db67bd0a 100644
> --- a/src/http/modules/ngx_http_grpc_module.c
> +++ b/src/http/modules/ngx_http_grpc_module.c
> @@ -1462,6 +1462,12 @@ ngx_http_grpc_body_output_filter(void *data, ngx_chain_t *in)
> in = in->next;
> }
>
> + ngx_chain_t *nl;
> + for (ngx_chain_t *dl = ctx->in; dl != in; dl = nl ) {
> + nl = dl->next;
> + ngx_free_chain(r->pool, dl);
> + }
> +
> ctx->in = in;
>
> if (last) {
>
> --------------------------------------------------------------------------------------------------------------------------------------------
>
> Best regards,
> Sangmin
> _______________________________________________
> nginx-devel mailing list
> nginx-devel at nginx.org
> https://mailman.nginx.org/mailman/listinfo/nginx-devel
--
Roman Arutyunyan
-------------- next part --------------
# HG changeset patch
# User Roman Arutyunyan <arut at nginx.com>
# Date 1716386385 -14400
# Wed May 22 17:59:45 2024 +0400
# Node ID 95af5fe4921294b48e634defc03b6b0f0201d6f7
# Parent e60377bdee3d0f8dbd237b5ae8a5deab2af785ef
Optimized chain link usage (ticket #2614).
Previously chain links could sometimes be dropped instead of being reused,
which could result in increased memory consumption during long requests.
A similar chain link issue in ngx_http_gzip_filter_module was fixed in
da46bfc484ef (1.11.10).
Based on a patch by Sangmin Lee.
diff --git a/src/core/ngx_output_chain.c b/src/core/ngx_output_chain.c
--- a/src/core/ngx_output_chain.c
+++ b/src/core/ngx_output_chain.c
@@ -117,7 +117,10 @@ ngx_output_chain(ngx_output_chain_ctx_t
ngx_debug_point();
- ctx->in = ctx->in->next;
+ cl = ctx->in;
+ ctx->in = cl->next;
+
+ ngx_free_chain(ctx->pool, cl);
continue;
}
@@ -203,7 +206,10 @@ ngx_output_chain(ngx_output_chain_ctx_t
/* delete the completed buf from the ctx->in chain */
if (ngx_buf_size(ctx->in->buf) == 0) {
- ctx->in = ctx->in->next;
+ cl = ctx->in;
+ ctx->in = cl->next;
+
+ ngx_free_chain(ctx->pool, cl);
}
cl = ngx_alloc_chain_link(ctx->pool);
diff --git a/src/http/modules/ngx_http_grpc_module.c b/src/http/modules/ngx_http_grpc_module.c
--- a/src/http/modules/ngx_http_grpc_module.c
+++ b/src/http/modules/ngx_http_grpc_module.c
@@ -1459,7 +1459,10 @@ ngx_http_grpc_body_output_filter(void *d
last = 1;
}
+ cl = in;
in = in->next;
+
+ ngx_free_chain(r->pool, cl);
}
ctx->in = in;
diff --git a/src/http/modules/ngx_http_gunzip_filter_module.c b/src/http/modules/ngx_http_gunzip_filter_module.c
--- a/src/http/modules/ngx_http_gunzip_filter_module.c
+++ b/src/http/modules/ngx_http_gunzip_filter_module.c
@@ -333,6 +333,8 @@ static ngx_int_t
ngx_http_gunzip_filter_add_data(ngx_http_request_t *r,
ngx_http_gunzip_ctx_t *ctx)
{
+ ngx_chain_t *cl;
+
if (ctx->zstream.avail_in || ctx->flush != Z_NO_FLUSH || ctx->redo) {
return NGX_OK;
}
@@ -344,8 +346,11 @@ ngx_http_gunzip_filter_add_data(ngx_http
return NGX_DECLINED;
}
- ctx->in_buf = ctx->in->buf;
- ctx->in = ctx->in->next;
+ cl = ctx->in;
+ ctx->in_buf = cl->buf;
+ ctx->in = cl->next;
+
+ ngx_free_chain(r->pool, cl);
ctx->zstream.next_in = ctx->in_buf->pos;
ctx->zstream.avail_in = ctx->in_buf->last - ctx->in_buf->pos;
@@ -383,8 +388,12 @@ ngx_http_gunzip_filter_get_buf(ngx_http_
conf = ngx_http_get_module_loc_conf(r, ngx_http_gunzip_filter_module);
if (ctx->free) {
- ctx->out_buf = ctx->free->buf;
- ctx->free = ctx->free->next;
+
+ cl = ctx->free;
+ ctx->out_buf = cl->buf;
+ ctx->free = cl->next;
+
+ ngx_free_chain(r->pool, cl);
ctx->out_buf->flush = 0;
diff --git a/src/http/modules/ngx_http_gzip_filter_module.c b/src/http/modules/ngx_http_gzip_filter_module.c
--- a/src/http/modules/ngx_http_gzip_filter_module.c
+++ b/src/http/modules/ngx_http_gzip_filter_module.c
@@ -985,10 +985,12 @@ static void
ngx_http_gzip_filter_free_copy_buf(ngx_http_request_t *r,
ngx_http_gzip_ctx_t *ctx)
{
- ngx_chain_t *cl;
+ ngx_chain_t *cl, *next;
- for (cl = ctx->copied; cl; cl = cl->next) {
+ for (cl = ctx->copied; cl; cl = next) {
ngx_pfree(r->pool, cl->buf->start);
+ next = cl->next;
+ ngx_free_chain(r->pool, cl);
}
ctx->copied = NULL;
diff --git a/src/http/modules/ngx_http_ssi_filter_module.c b/src/http/modules/ngx_http_ssi_filter_module.c
--- a/src/http/modules/ngx_http_ssi_filter_module.c
+++ b/src/http/modules/ngx_http_ssi_filter_module.c
@@ -482,9 +482,13 @@ ngx_http_ssi_body_filter(ngx_http_reques
while (ctx->in || ctx->buf) {
if (ctx->buf == NULL) {
- ctx->buf = ctx->in->buf;
- ctx->in = ctx->in->next;
+
+ cl = ctx->in;
+ ctx->buf = cl->buf;
+ ctx->in = cl->next;
ctx->pos = ctx->buf->pos;
+
+ ngx_free_chain(r->pool, cl);
}
if (ctx->state == ssi_start_state) {
diff --git a/src/http/modules/ngx_http_sub_filter_module.c b/src/http/modules/ngx_http_sub_filter_module.c
--- a/src/http/modules/ngx_http_sub_filter_module.c
+++ b/src/http/modules/ngx_http_sub_filter_module.c
@@ -335,9 +335,13 @@ ngx_http_sub_body_filter(ngx_http_reques
while (ctx->in || ctx->buf) {
if (ctx->buf == NULL) {
- ctx->buf = ctx->in->buf;
- ctx->in = ctx->in->next;
+
+ cl = ctx->in;
+ ctx->buf = cl->buf;
+ ctx->in = cl->next;
ctx->pos = ctx->buf->pos;
+
+ ngx_free_chain(r->pool, cl);
}
if (ctx->buf->flush || ctx->buf->recycled) {
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